Methods for preparing particle precursor, and particle precursor prepared thereby

ABSTRACT

The invention relates to a method for preparing core-shell structured particle precursor under a co-precipitation reaction. In this method, by controlling the feeding of different types of anion compositions and/or cation compositions, and adjusting the pH to match with the species, precipitated particles are deposited to form a precipitated particle slurry, filtering, and drying the precipitated particle slurry to yield the particle precursor. The invention also provides a particle precursor which includes a core-shell structure. The shell is made of gradient anions and/or cations. Such particle precursor can be used to prepare cathode of lithium-ion battery.

TECHNICAL FIELD

The present disclosure relates to a method for preparing a lithium-ionbattery cathode, particularly, to a method for preparing particleprecursor without using organic chelating additives to alter theprecipitation rates, and a particle precursor prepared by the methodabove, and also relates to a method for preparing cathode activeparticles therefrom.

BACKGROUND ART

The lithium-ion battery, originally commercialized in early 1990s, hascome to dominate the energy storage market for hand-held, electronicconsumer devices. This is because the battery is rechargeable and hashigh mass and volume energy density. Lithium-ion batteries are alsobeing extensively investigated for electric vehicle applicationscurrently. In electric vehicles, it is desirable that the batterycathode has high capacity, high power, improved safety, long cycle life,low toxicity and lower production costs. However, current cathodematerials generally fail to meet all these requirements.

One reason why current cathode material fails to meet all the desiredcharacteristics is that it is difficult to process complex multi-metalmaterials. As a matter of fact, one method suitable for processingcertain transition-metal elements may not suit for processing othertransition-metal elements which are desired to be integrated into thecathode particles. Hence, at such circumstance, other additives oragents would be needed to join the processing. For example, whenpreparing transition-metal precursor particles by a co-precipitationprocess, Ni—Mn—Co (abbr. NMC) is desired to be combined with aluminum(abbr. Al) to form the cathode precursor particles. However, Al wouldnot precipitate homogeneously with the Ni—Mn—Co under conventionalhydroxide processing conditions. Hence, complicated additives andcomplexing agents would have to be added into the reactor and join thereaction therein. This would bring the following disadvantages: first,the costs would be increased due to the feeding of the additives andcomplexing agents; second, removal of such additives and complexingagents would need extra work and would lead to waste of water.

When synthesizing NMC particles by such co-precipitation method, severalanion species would inevitably exist therein, such as oxalate, carbonateand hydroxide. Generally, hydroxide is the most preferable anion whenusing the co-precipitation method in industry, since it yieldshigh-density particles. Such high-density particles are beneficial forhigh energy density cells. However, the existence of such anions woulddo no good for the improvement of cathode electrochemical performancesince they would lead to changes in porosity, crystallite size, or localatomic ordering. To achieve high electrochemical performance, it isdesirable to select suitable processing conditions for certain cathodeelement (i.e., Al) combinations based on electrochemical differences ofvarious co-precipitation anions.

However, the addition of Al into the metal hydroxide cathode precursoris challenging. The solubility product constant (Ksp) of Al is orders ofmagnitudes lower at the pH ranges typically of NMC based particles,which result in fast and excessive precipitation and unusual secondaryparticle growth. As examples, four conventional methods of depositing Alare described below.

U.S. Pat. No. 9,406,930B discloses a method to deposit NCA (abbr.Ni—Co—Al) compositions as a shell on a core of NMC nucleates, duringwhich the pH value is adjusted to a lower value to facilitate thedeposition of Al. As a matter of fact, the pH value of below 10 issuitable for Al deposition. However, in such method, the pH value is 12to 14 at a reference liquid temperature of 25° C., much higher than 10.Hence, such method results in uneven Al deposition and needs longreaction time, which leads to greatly cumulated particle surface area.None of these is desirable.

U.S. Pat. No. 8,216,676B2 discloses a method in which Al is deposited onLiCoO₂, LiMn₂O₄ and NMC cathode active material particles. During whichthe ratio of Co to the transition metal is controlled to be greater than50% while adjusting the pH near 9. As a result, the coating is onlypresent on the particle surface, not within the particle during thedeposition, which is performed on a final material. Hence, such methodfails to integrate Al within the particle structure, especially forNi-rich materials with little or no Co present.

U.S. Pat. No. 9,876,226B provides precursor cathode particles which aredry-coated with smaller alumina particles. Such method relies on Al ionsto diffuse into the structure during heating. However, for Ni-richcathode materials, high heat treatment would result in formation ofinactive rock-salts, which degrades the cathode performance. Hence, itis typically not desirable.

CN106207140A discloses a method in which the aluminum (Al) is addedduring co-precipitation to NC (abbr. Ni—Co) materials at the existenceof a special complexing agent or chelator. Such complexing agent bringscomplexity to the process, and results in additional treatment of wastewater. The feeding of organic chelator would adversely affect thereaction time. However, such method fails to avoid using such complexingagent or chelator.

Meanwhile, another problem to achieve high electrochemical performanceis that during the preparation of active material, water produced fromhydroxide-based cathodes would cause corrosion to processing equipment,which may damage the cathode particle performance, since high watervapor contents are associated with large grains observed on theparticles after calcination. Generally, one method to solve such problemis to increase the volumetric flowrates of the reaction gas within thereactor. However, it could only accelerate the removal rate, but failsto mitigate the water generation. Further, such method also increasesproduction costs, and could not reduce the downstream corrosion. Infact, in some cases the corrosion may increase since more oxidative gasis used. On one hand, using much oxidative gas could promote the waterremoval, on the other hand, it could also increase the corrosion to theprocessing unit. Hence, removal of some water generation under thepremise of not leading to corrosion is still not solved.

Further, there is still other problem remained unsolved for lithium-ioncathode materials. On one hand, since cobalt (abbr. Co) performs adumbbell configuration due to the movement of its atoms, suchconfiguration makes the movement of Ni/Li switching hard, which in turnblock the migration path of the Ni and Li. Because of this, Co decreasesthe site exchange between the transition metals such as Ni to Li, andfurther benefit for better electrochemical performance. On the otherhand, transition metal composition, such as Co, has a major influence onthe costs since Co is the most expensive transition metal. Hence, it isdesirable to abandon Co from the structure of cathode particles whileimproving the electrochemical performance simultaneously.

Technical Problem

First, it is difficult to add Al into metal hydroxide cathode precursorwhile achieving high electrochemical performance. Second, during thepreparation of active particles, water produced from hydroxide-basedcathodes would cause corrosion to the equipment. Third, Co is expensivewhich makes the cost much higher.

Technical Solution

The present disclosure provides a method for preparing core-shellstructured particle precursor, the core-shell structured particleprecursor may be combined with metals such as lithium to form cathodeactive particles which can be used for lithium-ion batteries.

The method for preparing a core-shell structured particle precursorincludes at least the following steps: from an initial time t₀ to afirst time t₁, feeding a first anion composition B₁ through a firstcontainer into a reactor, and feeding a first cation composition A₁through a second container into the reactor, the first anion compositionB₁ and the first cation composition A₁ reacting and precipitating in thereactor, t₁ comes after t₀, t₀=0; at the first time t₁, the firstcontainer is full of the first anion composition B₁, the secondcontainer is full of the first cation composition A₁; feeding a secondanion composition B₂ and the first anion composition B₁ through thefirst container into the reactor from the first time t₁ to a second timet₂, t₂ comes after t₁, during which the first anion composition B₁ isgradually switched to the second anion composition B₂; and feeding atleast the first cation composition A₁ through the second container intothe reactor from the first time t₁ to the second time t₂, therebyforming a precipitated particle slurry; and filtering, and drying theprecipitated particle slurry to yield the particle precursor.

In one embodiment, the step that the first anion composition B₁ isgradually switched to the second anion composition B₂ includes thefollowing steps: at the first time t₁, the first container is full ofthe first anion composition B₁; gradually feeding the second anioncomposition B₂ into the first container from the first time t₁ to asecond time t₂, t₂ comes after t₁, where the first anion composition B₁and the second anion composition B₂ form a dynamic mixture; and feedingthe dynamic mixture through the first container into the reactor fromthe first time t₁ to the second time t₂, at the second time t₂, thefirst container is mainly full of the second anion composition B₂.

In one embodiment, method further includes the following step: feedingthe second anion composition B₂ and the first cation composition A₁ intothe reactor from the second time t₂ to a third time t₃, t₃ comes aftert₂.

In one embodiment, during the initial time t₀ to the second time t₂,only the first cation composition A₁ is fed into the reactor.

In another embodiment, from the initial time t₀ to the first time t₁,only the first cation composition A₁ is fed through the second containerinto the reactor; and from the first time t₁ to the second time t₂,feeding a second cation composition A₂ and the first cation compositionA₁ through the second container into the reactor, during which the firstcation composition A₁ is gradually switched to the second cationcomposition A₂.

In still another embodiment, from the initial time t₀ to a switchingtime t_(s), only the first cation composition A₁ is fed through thesecond container into the reactor, t_(s) is between the first time t₁and the second time t₂; and from the switching time t_(s) to the secondtime t₂, feeding a second cation composition A₂ and the first cationcomposition A₁ through the second container into the reactor, duringwhich the first cation composition A₁ is gradually switched to thesecond cation composition A₂. The present disclosure still provides acore-shell structured particle precursor, which is prepared by themethods above. The core-shell structured particle precursor includes acore and a shell enwrapping the core, the core is made of precipitationsof a first anion composition B₁ and a first cation composition A₁, theshell is gradient and is made of co-precipitations of the first anioncomposition B₁, a second anion composition B₂ and at least the firstcation composition A₁, the first anion composition B₁ is graduallychanged to the second anion composition B₂ in the shell from inner toouter.

In one embodiment, the shell further includes a second cationcomposition A₂, the first cation composition A₁ is gradually changed tothe second cation composition A₂ within the shell.

In another embodiment, the particle precursor further includes aperiphery part enwrapping the shell, the periphery part is made ofprecipitations of the second anion composition B₂ and the first cationcomposition A₁.

In still another embodiment, the shell is divided into an intermediatepart and a gradient part based on the cations, the first anioncomposition B₁ is gradually changed to the second anion composition B₂within the shell, the intermediate part further includes the firstcation composition A₁, the gradient part further includes the firstcation composition A₁ and the second cation composition A₂, the firstcation composition A₁ is gradually changed to the second cationcomposition A₂ within the gradient part. In any of the embodiment ofthis invention, at time t₁ when the second anion composition B₂ is to befed into the first container, the description “the first container isfull of the first anion composition B₁” is not just mean that there isonly the first anion composition B₁ in the first container but mean thatthe container has the first anion composition B₁ and also small amountof the second anion composition B₂ at the critical time t₁.

In any of the embodiment of this invention, at time t₁ and/or t_(s) whenthe second cation composition A₂ needs to be fed into the secondcontainer, the description “the first container is full of the firstcation composition A₁” does not just mean that there is only the firstcation composition A₁ in the first container but means that besides thefirst cation composition A₁, there is also small amount of the secondcation composition A₂ at the critical time t₁ and/or t_(s).

In any of the embodiment of this invention, at the time t₁, t₂, and/ort₃, when adding the second anion composition B₂, there may still exitssmall amount of the first anion composition B₁ in the first container.In any of the embodiment of this invention, at the time t₁, t₂, and/ort_(s), when adding the second cation composition A₂, there may stillexits small amount of the first cation composition A₁ in the firstcontainer.

Advantageous Effects

The method of the present disclosure has the following advantages:

Firstly, since different cations can be precipitated with differentanions separately, the transition metal cations (dopants) that areincompatible with the core anion species under the processing conditionscan be easily added to the particle precursor in the shell. And viceversa, wherein cations or other dopants that can only be compatible withthe core anion under the processing conditions can be added to theparticle before switching to an incompatible processing location for theshell. Particularly, Al³⁺ can be added to the particle precursor duringthe co-precipitation under the premise that there is hydroxide in thesolution which can form precipitation with Al³⁺; in such conditions, noadditional organic chelating additives are needed to remove Al³⁺, andthe precipitation kinetics are avoided to be slowed without chelatingagents. Because of this, Ni-rich particles precursor can have Al dopantinto the particle without using organic chelating additives, the Ni-richparticles precursor has a mole ratio of Ni to transitional metals higherthan 0.7. The concentration of Al³⁺ deposited into the particles can beadjusted based on the time feeding the Al³⁺ dopants and the time whenswitching the anions.

Secondly, no matter where the gradient portion is located, in the coreor in the shell, the concentration gradient of the anion species ensuresthat the transition between different anion species is smooth, that is,the transition from the former anion to the latter is not a sharpchange, but a gradual switching. Because of this, the gradient portionendows the particle precursor a gradient surface, which makes thetransition from the portion having only the first anion to the portionhaving both the first and second anions becomes more smoothly. Theparticle precursor is more solid during later processing, and cracks ordelamination would not occur. This has great improved the duration andlife-span of the cathode particles prepared based on the particleprecursor.

Thirdly, due to the feeding of elements Ni, Mn, Al etc. into thereaction, the cobalt content will be below 20% of the total transitionmetal ratio, and preferably below 5%, and more preferably 0% cobalt willbe present in the cathode precursor particle. Because of this, the costis greatly decreased.

DESCRIPTION OF DRAWINGS

FIG. 1 shows a schematic view of the reaction device to form thefull-gradient particle precursors in one embodiment of the presentdisclosure.

FIG. 2 shows a schematic view of a core-shell structured particleprecursor of a first example, which has a core and a shell enwrappingthe core, the core is made of only a first anion B₁, the shell is madeof the first anion B₁ and a second anion B₂, in which the first anion B₁is gradually switched to the second anion B₂, meanwhile a first cationA₁ is constant both in the core and the shell.

FIG. 3 shows a schematic view of a core-shell structured particleprecursor of a second example, which has a core and a shell enwrappingthe core, the core is made of a first anion B₁ and a first cation A₁,and the shell is made of the first anion B₁ and a second anion B₂, andthe first cation A₁ and the second cation A₂, in which the first anionB₁ is gradually switched to the second anion B₂, meanwhile the firstcation A₁ is also gradually switched to the second cation A₂.

FIG. 4 shows a schematic view of a core-shell structured particleprecursor of a third example, which has a core and a shell enwrappingthe core, the core includes a first anion B₁ and a first cation A₁; theshell includes the first anion B₁, a second anion B₂, the first cationA₁ and a second cation A₂, in which the first anion B₁ is graduallyswitched to the second anion B₂, meanwhile the first cation A₁ isconstant for a certain period and then gradually switched to the secondcation A₂.

FIG. 5 shows a schematic view of a core-shell structured particleprecursor of a fourth example, which has a core and a shell, a firstcation A₁ is constant through the particle precursor, meanwhile the coreincludes a first anion B₁, the shell includes the first anion B₁ and asecond anion B₂, in which the first anion B₁ is gradually switched tothe second anion B₂ in the shell; meanwhile, the particle precursorfurther includes an outer part enwrapping the shell, and the outer partincludes the second anion B₂ and the first cation A₁.

FIG. 6 shows SEM image of cross-sectional particle precursors ofEmbodiment 1.

FIG. 7 shows carbon intensity derived from the SEM image ofcross-sectional particle precursors of Embodiment 1.

MODE FOR THE INVENTION

The present disclosure will now be described more specifically withreference to the following embodiments. It is to be noted that thefollowing descriptions of preferred embodiments of this invention arepresented herein for purpose of illustration and description only. It isnot intended to be exhaustive or to be limited to the precise formdisclosed.

In the embodiments below, particle precursors with anion-gradientcore-shell structures will be prepared by a co-precipitation reaction,and the solution volume where the reaction takes place is defined as aprecipitation zone.

The method for preparing such anion-gradient core-shell structuredparticle precursors includes the following steps: firstly, vacuuming theprecipitation zone and/or filling with He, N₂ or Ar gas, for example,blanketing or bubbling the precipitation zone by He, N₂ or Ar gas.

Next, introducing a stream (b) into a reactor for providingprecipitating anions, feeding stream (a) for providingtransitional-metal cations, whereby the precipitating anions and thetransitional-metal cations react to form a precipitated particle slurry;the stream (a) includes at least a first cation composition A₁; thestream (b) includes at least a first anion composition B₁ and a secondanion composition B₂, both are fed simultaneously from an initial timet₀ to a second time t₂, a concentration of the first anion compositionB₁ is constant from the initial time t₀ to a first time t₁, and then thefirst anion composition B₁ is gradually switched to the second anioncomposition B₂ from the first time t₁ to the second time t₂, in which t₁comes after to and t₂ comes after t₁. The initial time t₀ refers to atime when the first cation A₁ and the first anion B₁ are initially fedinto the reactor and starts to precipitate, t₀=0. The first time t₁refers to a critical time when both the first anion B₁ and the secondanion B₂ start to be fed into the reactor and co-precipitation occurs.

Finally, filtering and drying the precipitated particle slurry to yieldthe particle precursor.

Particularly, the feeding of the stream (b) is as follows: firstly,feeding the first anion composition B₁ through a first container intothe rector from the initial time t₀ to the first time t₁; since thefirst container have certain space to occupy liquids, it is filled withthe first anion composition B₁ when reaching the first time t₁;secondly, feeding the second anion composition B₂ through a thirdcontainer into the first container at a certain flowrate from the firsttime t₁ to the second time t₂, hence, the first anion composition B₁ andthe second anion composition B₂ form a dynamic mixture in the firstcontainer, which is fed into the reactor through the first containerfrom the first time t₁ to the second time t₂. At the second time t₂, thedynamic mixture includes mainly the second anion composition B₂. Hence,during such step, from the initial time t₀ to the first time t₁, thefirst anion composition B₁ is the only anion that is fed into thereactor, while from the first time t₁ to the second time t₂, the firstanion composition B₁ is gradually switched to the second anioncomposition B₂.

FIG. 1 shows a flow diagram of the method above in one embodiment. Asshown in FIG. 1 , in such embodiment, the first anion composition B₁ isfed through a first container directly to the reactor, while the secondanion composition B₂ is continuously fed from the third container intothe first container and mixed with the first anion composition B₁ toform a dynamic mixture in the first container, and then the dynamicmixture is further fed through the first container into the reactor.

In one embodiment, the first anion composition B₁ has a constantflowrate or concentration from the initial time t₀ to the first time t₁.

In the process of the present disclosure, the stream (b) functions toprovide anions which would enter the precipitation particles, theconcentration of the anions in stream (b) is 0.001-14 (mol anion/L).Meanwhile, the anion composition B; (i=1, 2, . . . ), i.e., B₁, or B₂ isselected from the group consisting of NaOH, Na₂CO₃, NaHCO₃, Na₂C₂O₄,LiOH, Li₂CO₃, LiHCO₃, Li₂C₂O₄, KOH, K₂CO₃, KHCO₃, K₂C₂O₄ or somecombination of the species listed above. In one embodiment, the firstanion composition B₁ is a solution entirely configured from hydroxidesalts. In another embodiment, the second anion composition B₂ includes[CO₃] salts, [C₂O₄] salts, [OH] salts, or some combination of thespecies listed.

In one embodiment, the first anion composition B₁ includes hydroxideanion, a content of the hydroxide anion in the stream (b) is no lessthan 80 wt %. The second anion composition B₂ includes carbonate anionand/or oxalic anion, a content of the carbonate and/or oxalic anions isno less than 40 wt % in the steam (b).

With regard to the cations, in the present disclosure, stream (a)functions to provide transitional-metal cations. Stream (a) includes thecations for precipitation with a concentration from 0.001-6 molcation/L. The cations provided by stream (a) is at least one selectedfrom the group consisting of Mg, Ca, Zr, Ti, V, Cr, Mn, Fe, Co, Ni, Cu,Al or some combination of the species listed above. The cation(s)provided by stream (a) is in a form of sulfate, carbonate, chloride,nitrate, fluoride, oxide, hydroxide, oxyhydroxide, oxalate, carboxylateor acetate, phosphate or borate.

Stream (a) has at least one cation composition species. In oneembodiment, for example, as shown in FIGS. 2 and 5 , stream (a) only hasone cation, i.e., a first cation composition A₁. In another embodiment,for example, as shown in FIGS. 3-4 , the stream (a) has a first cationcomposition A₁ and a second cation composition A₂. Optionally, duringthe method for preparing the core-shell structure particle precursor,additional streams (e . . . z) may also be introduced into the reactorto add additional species to the reaction, or to remove solvent throughan in-situ thickening device.

Please note that in the present disclosure, the “core” and “shell” arenamed merely based on the anions distribution.

The method above produces a core-shell structured particle precursor,which includes a core and a shell enwrapping the core, as shown in FIGS.2-5 . The core is in the center of the particle precursor, which is madeof precipitations formed by the first anion composition B₁ and the firstcation composition A₁ from the initial time t₀ to the first time t₁, thefirst anion composition B₁ and the first cation composition A₁ haveuniform concentration separately. The shell is in the periphery of thecore, which is made of co-precipitations formed by the first anioncomposition B₁, the second anion composition B₂ and at least the firstcation composition A₁, in which the first anion composition B₁ isgradually switched to the second anion composition B₂ from inner toouter.

In detail, in one embodiment, as shown in FIG. 2 , the core-shellstructured particle precursor includes a core and a shell, the core ismade of precipitations formed by the first anion composition B₁ and thefirst cation composition A₁ fed from the initial time t₀ to the firsttime t₁, the shell is made of co-precipitations formed by the firstanion composition B₁, the second anion composition B₂ and the firstcation composition A₁ fed from the first time t₁ to the second time t₂,in which the first anion composition B₁ is gradually switched to thesecond anion composition B₂, meanwhile the first cation composition A₁is constant.

As shown in FIG. 3 , in another embodiment, the core-shell structuredparticle precursor includes a core and a shell, the core is made ofprecipitations formed by the first anion composition B₁ and the firstcation composition A₁ fed from the initial time t₀ to the first time t₁,the shell is made of co-precipitations formed by the first anioncomposition B₁, the second anion composition B₂, the first cationcomposition A₁ and the second cation composition A₂ fed from the firsttime t₁ to the second time t₂, in which the first anion composition B₁is gradually switched to the second anion composition B₂, meanwhile thefirst cation composition A₁ is gradually switched to the second cationcomposition A₂.

As shown in FIG. 4 , in still another embodiment, the core-shellstructured particle precursor includes a core and a shell, the core ismade of precipitations formed by the first anion composition B₁ and thefirst cation composition A₁ fed from the initial time t₀ to the firsttime t₁, the shell is made of co-precipitations formed by the firstanion composition B₁, the second anion composition B₂, the first cationcomposition A₁ and the second cation composition A₂ fed from the firsttime t₁ to the second time t₂, in which the first anion composition B₁is gradually switched to the second anion composition B₂, meanwhile thefirst cation composition A₁ is still constant from the first time t₁ toa switching time t_(s), and then gradually switched to the second cationcomposition A₂ from the switching time t_(s) to the second time t₂. Theswitching time t_(s) is between the first time t₁ and the second timet₂.

Hence, the shell in FIG. 4 is divided into two parts due to thedifference in cations, i.e., a uniform cation part and a full-gradientcation part, the uniform cation part includes only the first cationcomposition A₁, and the full-gradient cation part includes the firstcation composition A₁ and the second cation composition A₂, in which thefirst cation composition A₁ is gradually switched to the second cationcomposition A₂ from the switching time t_(s) to the second time t₂.

As shown in FIG. 5 , in yet another embodiment, the core-shellstructured particle precursor includes three parts, a core, a shell anda periphery shell. The core and the shell are the same as that in FIG. 2. The difference from FIG. 2 is that the particle precursor in FIG. 5further includes the periphery shell which is made of precipitationsmade by the second anion composition B₂ and the first cation compositionA₁ fed from the second time t₂ to a third time t₃. The third time t₃refers to a time when the reaction ends.

In the embodiments of FIGS. 2-5 , during the precipitation of B₁ fromthe initial time t₀ to the first time t₁, the step of feeding the stream(b) includes the following step: feeding the first anion composition B₁through the first container to the reactor from the initial time t₀ tothe first time t₁, and the first container is in a state full of thefirst anion composition B₁.

During the co-precipitation of B₁ and B₂ from the first time t₁ to thesecond time t₂, at the first time t₁, the first container is filled withthe first anion composition B₁, the first container is connected withthe reactor; the step that the first anion composition B₁ is graduallyswitched to the second anion composition B₂ from the first time t₁ tothe second time t₂ includes the following steps: feeding the secondanion composition B₂ from the third container into the first containerwith a certain flowrate from the first time t₁ to the second time t₂,the first anion composition B₁ and the second anion composition B₂ forma dynamic mixture in the first container; and feeding the dynamicmixture into the reactor through the first container from the first timet₁ to the second time t₂, wherein at the first time t₁, the dynamicmixture fed into the reactor is mainly the first anion composition B₁,while at the second time t₂, the dynamic mixture is mainly the secondanion composition B₂.

Besides, in the embodiment of FIG. 5 , from the second time t₂ to thethird time t₃, the second anion composition B₂ is further fed throughthe first container into the reactor.

Generally, the instantaneous concentration of anions being fed into thereactor from the first time t₁ to the second time t₂ can be describedas:

${B = \frac{{B_{i}V_{i}} + {\left( {{F_{B2}B2} - {B_{i}F_{B}}} \right)\left( {t_{i + 1} - t_{i}} \right)}}{V_{i + 1}}},$where B is the instantaneous concentration of anions being fed into thereactor, B_(i) is the anion concentration at time t_(i) that exists inthe first container, V_(i) is the volume of solution at time t_(i) thatexists in the first container, F_(B2) is the flowrate from the thirdcontainer into the first container, B2 is the anion concentration in thethird container, F_(B) is the flowrate from the first container into thereactor, t_(i+1) is time at moment i+1, t_(i) is time at moment i,V_(i+1) is the volume of solution at time t_(i+1) that exists in thefirst container.

In one embodiment, before the first time t₁, the first anion compositionB₁ is fed uniformly, after the first time t₁, the first anioncomposition B₁ is gradually altered to the second anion composition B₂at the second time t₂.

In one embodiment, the first time t₁ is greater than 50% of the wholereaction time. In another embodiment, the first time t₁ is greater than75% of the whole reaction time.

In one embodiment, the time period from the initial time t₀ to the firsttime t_(i) is greater than 50% of the whole reaction time. In anotherembodiment, the time period from the initial time t₀ to the first timet_(i) is greater than 75% of the whole reaction time.

In one embodiment, the flowrate or concentration of stream (b) areconstant during the co-precipitation reaction before the first time t₁.In another embodiment, the flowrate or concentration of stream (b) isgradually changed during the reaction. In still another embodiment, theflowrate and the concentration begin to change from the first time t₁when the first anion composition B₁ is gradually changed to the secondanion composition B₂.

In the embodiment of FIG. 3 , during the precipitation of A₁ from theinitial time t₀ to the first time t₁, the step of feeding the stream (a)includes the following step: feeding the first cation composition A₁through the second container to the reactor from the initial time t₀ tothe first time t₁, during which the first cation composition A₁ is alsofilled into the second container, which makes the second container in astate full of the first cation composition A₁ at the first time t₁.Because of this, the core is formed to have the first cation compositionA₁ as the only cation with uniform concentration.

During the co-precipitation of A₁ and A₂ from the first time t₁ to thesecond time t₂, in which at the first time t₁, the second container isfilled with the first cation composition A₁, the second container isconnected with the reactor; the step that the first cation compositionA₁ is gradually switched to the second cation composition A₂ from thefirst time t₁ to the second time t₂ includes the following steps:feeding the second cation composition A₂ from a fourth container intothe second container with a certain flowrate from the first time t₁ tothe second time t₂, the first cation composition A₁ and the secondcation composition A₂ form a dynamic mixture in the second container;and feeding the dynamic mixture into the reactor through the secondcontainer from the first time t₁ to the second time t₂, wherein at thefirst time t₁, the dynamic mixture fed into the reactor is mainly thefirst cation composition A₁, while at the second time t₂, the dynamicmixture is mainly the second cation composition A₂.

In the embodiment of FIG. 4 , during the precipitation of A₁ from theinitial time t₀ to the switching time t_(s), the step of feeding thestream (a) includes the following step: feeding the first cationcomposition A₁ through the second container to the reactor from theinitial time t₀ to the switching time t_(s), during which the firstcation composition A₁ is also filled into the second container, whichmakes the second container in a state full of the first cationcomposition A₁ at the switching time t_(s).

During the co-precipitation of A₁ and A₂ from the switching time t_(s)to the second time t₂, in which at the switching time t_(s), the secondcontainer is filled with the first cation composition A₁, the secondcontainer is connected with the reactor; the step that the first cationcomposition A₁ is gradually switched to the second cation composition A₂from the switching time t_(s) to the second time t₂ includes thefollowing steps: feeding the second cation composition A₂ from thefourth container into the second container with certain flowrate fromthe switching time t_(s) to the second time t₂, the first cationcomposition A₁ and the second cation composition A₂ form a dynamicmixture in the second container; and feeding the dynamic mixture intothe reactor through the second container from the switching time t_(s)to the second time t₂, wherein at the switching time t_(s), the dynamicmixture fed into the reactor is mainly the first cation composition A₁,while at the second time t₂, the dynamic mixture is mainly the secondcation composition A₂.

In the embodiment of FIG. 2 , the first cation composition A₁ is fedfrom the initial time t₀ to the second time t₂. In the embodiment ofFIG. 5 , the first cation composition A₁ is fed from the initial time t₀to the third time t₃.

In the embodiments of the present disclosure, the first cationcomposition A₁ and the second cation composition A₂ has a cation ratioof Ni_(x)Mn_(y)Co_(z)Me_(1-x-y-z), where x+y+z≥0.9, z≤0.2, and “Me”refers to one or more additional metal elements selected from the groupconsisting of Mg, Ca, Zr, Ti, V, Cr, Fe, Cu and Al. In one embodiment,z<0.05. In another embodiment, z=0. In another embodiment, “Me” is Al,Mg, Zr, Ti or some combination of the species listed above.

Please note that in the particle precursor product, the “first anioncomposition B₁”, “second anion composition B₂ ^(”) and “third anioncomposition B₃ ^(”) refers to the anion precipitated therein. Meanwhile,the “first anion composition B₁”, “second anion composition B₂ ^(”) and“third anion composition B₃ ^(”) in the method refers to the saltscontaining the anions mentioned.

The present disclosure further provides a method for preparing cathodeactive particles, which includes the steps below: after yielding theparticle precursors above, mixing the particle precursors with a lithiumsource to form a mixture, and calcining the mixture to yield cathodeactive particles. During such calcination, lithiation reaction occurredand water removed from the mixture.

Generally, each precipitation zone volume is defined as the volume of asingle mixed vessel or the sum of several processing vessels, pumps, orsolid-liquid thickening devices connected in parallel.

The precipitation zone can generally be described by the following massbalance equation:

${\frac{d\left( {\rho_{c}V} \right)}{dt} = {\Sigma_{\alpha = a}^{z}F_{\alpha}\rho_{\alpha}}},$where “α” represents for the inlet/outlet streams (a) to (z), “ρ_(α)”represents for a fluid density, “V” refers to a volume of theprecipitation zone, “F_(α)” refers to a flowrate of the volumetric,“ρ_(α)” is a density of inlet streams; “ρ_(c)” is a density ofaccumulating fluid in the reactor which changes with time.

In one embodiment, only one precipitation zone is used, and theco-precipitation reactions occur during batch operation, the massbalance equation is defined as d(ρ_(c)V)/dt≠0.

In another embodiment, multiple precipitation zones are linked inseries, d(ρ_(c)V)/dt≠0. In still another embodiment, multipleprecipitation zones are linked in series, d(ρcV)/dt=0.

In the present disclosure, the cathode active particles are core-shellstructured particle precursor produced by a co-precipitation reaction,size of the cathode active particles is proportional to the reactiontime, and the composition deposited onto a particle at a particular timeis directly related to the inlet ion compositions.

As shown in FIG. 2 , the particle precursor has a core-shell structure,from the initial time t₀ to the first time t₁, the first anioncomposition B₁ and the first cation composition A₁ are fed into thereactor. Because of this, the core is made of the precipitations formedby the first anion composition B₁ and the first cation composition A₁.From the first time t₁ to the second time t₂, the first anioncomposition B₁ is gradually changed to the second anion composition B₂,and the first cation composition A₁ is still fed into the reactor at aconstant flowrate or concentration. In this embodiment, the shell ismade of precipitations formed by the first anion composition B₁, thesecond anion composition B₂ and the first cation composition A₁, inwhich the first anion composition B₁ is gradually switched to the secondanion composition B₂, while the first cation composition A₁ is constant.

As shown in FIG. 3 , the particle precursor includes a core-shellstructure. In such embodiment, from the initial time t₀ to the firsttime t₁, only the first cation composition A₁ and the first anioncomposition B₁ are fed into the reactor. From the first time t₁ to thesecond time t₂, the first cation composition A₁ is gradually changed tothe second cation composition A₂, and the first anion composition B₁ isgradually changed to the second anion composition B₂. In thisembodiment, the shell is formed by co-precipitation particles whichincludes the first anion composition B₁ and the second anion compositionB₂, and the first cation composition A₁ and the second cationcomposition A₂, in which the first anion composition B₁ is graduallychanged to the second anion composition B₂, while the first cationcomposition A₁ is gradually changed to the second cation composition A₂;the core is formed by precipitation particles which includes the firstanion composition B₁ and the first cation composition A₁.

In still another embodiment, as shown in FIG. 4 , the stream (a) has thefirst cation composition A₁ and the second cation composition A₂. Fromthe initial time t₀ to the switching time t_(s), the first cationcomposition A₁ is constant, while from the switching time t_(s) to thesecond time t₂, the first cation composition A₁ is gradually changed tothe second cation composition A₂. Meanwhile, from the initial time t₀ tothe first time t₁, the first anion composition B₁ is constant; from thefirst time t₁ to the second time t₂, the first anion composition B₁ isgradually changed to the second anion composition B₂. Because of this,at the time period from the first time t₁ to the switching time t_(s),the shell includes an intermediate part which is formed by precipitationparticles formed by anions of the first anion composition B₁ and thesecond anion composition B₂, and cations of the first cation compositionA₁.

In this embodiment, the core is formed to have only the first cationcomposition A₁ and the first anion composition B₁ with constantconcentration. Within the shell, it includes the first anion compositionB₁ and the second anion composition B₂, in which the first anioncomposition B₁ is gradually changed to the second anion composition B₂.Further, the shell is divided to an intermediate part and a gradientpart based on the cations. The intermediate part is formed byco-precipitation particles which include the first cation compositionA₁; the gradient part is formed by co-precipitation particles whichinclude the first cation composition A₁ and the second cationcomposition A₂, in which the first cation composition A₁ is graduallychanged to the second cation composition A₂.

In yet another embodiment, as shown in FIG. 5 , different from that inFIG. 2 , the particle precursor further includes a periphery partenwrapping the shell. The periphery part is made of precipitations ofthe second anion composition B₂ and the first cation composition A₁.

In view of the above, in one embodiment, the cation composition changesfrom the first composition A₁ to the second composition A₂ gradually asa gradient with time. In another embodiment, the cation compositionchanges from the first composition A₁ to the second composition A₂abruptly, as a core-shell interface. The second time when A₁ switches toA₂ can occur at any moment. In one embodiment, the time when the cationcomposition switches from the first composition A₁ to the secondcomposition A₂ does not coincide with the time when the anioncomposition changes from B₁ to B₂.

In one embodiment, A₁=A₂. In such embodiment, there is only one cationcomposition species in stream (a) fed into the reactor from thebeginning to the end. For example, in one embodiment, as shown in FIGS.2 and 5 .

In another embodiment, as shown in FIG. 3 , the cation compositionchanges from the first composition A₁ to the second composition A₂ forfeeding different transitional-metal combinations will start at the sametime period when the anion composition changes from the firstcomposition B₁ to the second composition B₂ for feeding different anionsdeposited into the active particles, i.e., from the first time t₁ to thesecond time t₂. In this embodiment, since the cation composition and theanion composition change at the same time, the deposited activeparticles will have a core-shell structure, the core of the particleincludes the first cation composition A₁ and the first anion compositionB₁, and the shell of the particle enwraps around the core and includesthe first cation composition A₁ and the second cation composition A₂,and the first anion composition B₁ and the second anion composition B₂,wherein the first cation composition A₁ is gradually changed to thesecond cation composition B₂, and the first anion composition B₁ isgradually changed to the second anion composition B₂. FIG. 3 shows aschematic view of the particle precursor where the first cation A₁ andthe first anion B₁ is in the core, and the first cation A₁ and secondcation A₂, and the first anion B₁ and second anion B₂ is in the shell.

Further, either of the first cation composition A₁ and the second cationcomposition A₂ has a cation ratio of Ni_(x)Mn_(y)Co_(z)Me_(1-x-y-z),where x+y+z≥0.9, z≤0.2, and “Me” refers to one or more additional metalelements selected from the group consisting of Mg, Ca, Zr, Ti, V, Cr,Fe, Cu and Al. In one embodiment, z<0.05. In another embodiment, z=0. Inanother embodiment, “Me” is Al, Mg, Zr, Ti or some combination of thespecies listed above.

Under the feed conditions discussed above, a precipitated particleslurry will be collected after the co-precipitation is finished, afterbeing treated, the particle slurry is treated to yield the particleprecursor. The particle precursor is expressed as(Ni_(x)Mn_(y)Co_(z)Me_(1-x-y-z))(CO₃)_(a)(OH)_(2-2a) where x+y+z≥0.9,z≤0.2, 0≤a≤1, “Me” is additional metal elements except Ni, Mn and Co,such as Mg, Ca, Zr, Ti, V, Cr, Fe, Cu and Al.

In some embodiments, the first cation composition A₁ and the secondcation composition A₂ are different. In such embodiments, the firstcation composition A₁ has a cation ratio ofNi_(x)Mn_(y)Co_(z)Me_(1-x-y-z), where x+y+z≥0.9, 0.75≤x≤1; 0≤z≤0.1, “Me”refers to one or more additional metal elements selected from the groupconsisting of Mg, Ca, Zr, Ti, V, Cr, Fe, Cu and Al. The second cationcomposition A₂ has a cation ratio of Ni_(x)Mn_(y)Co_(z)Me_(1-x-y-z)where x+y+z≥0.9, 0.3≤x≤0.7; 0.25≤y≤0.5, “Me” refers to one or moreadditional metal elements selected from the group consisting of Mg, Ca,Zr, Ti, V, Cr, Fe, Cu and Al.

In one embodiment, by changing the composition of stream (a), cationcomposition would be changed continuously for all or part of thematerial, thus forming a cathode whose cation is made of concentrationgradient transitional-metals. In one embodiment, thetransitional-metals, i.e., the cations, change during the whole processfor preparing the entire particle. In another embodiment, only a portionof the particle make linear gradient shell transitional-metal particleswith a core-shell anion species, others remain same. In still anotherembodiment, only a portion of the particle make non-linear gradientshell transitional-metal particles with a core-shell anion species. Inyet another embodiment, only a portion of the particle make multi-slopegradient shell transitional-metal particles with a core-shell anionspecies. In still another embodiment, only a portion of the particlemake core-gradient shell transitional-metal particles with a core-shellanion species. In yet another embodiment, only a portion of the particlemake core-gradient-shell transition metal particles with a core-shellanion species.

In some embodiments, to obtain the gradient part of the shell, thetransitional-metal feed, i.e., the stream (a) which provides the firstcation composition A₁ and the second cation composition A₂ has a cationratio of Ni_(x)Mn_(y)Co_(z)Me_(1-x-y-z), where x+y+z≥0.9, z≤0.2, “Me”refers to one or more additional metal elements selected from the groupconsisting of Mg, Ca, Zr, Ti, V, Cr, Fe, Cu and Al, the first cationcomposition A₁ is selected from 0.85≤x≤1; 0≤z≤0.1, the second cationcomposition A₂ is selected from 0.4≤x≤0.7; 0.25≤y≤0.5.

In one embodiment, the start of gradient part in shell, or the change inslope for multi-slope cathode particles can occur at any time during theparticle process.

In one embodiment, as shown in FIG. 4 , the time when the first cationcomposition A₁ starts to gradually be switching to the second cationcomposition A₂ does not coincide with the time when the first anioncomposition B₁ starts to gradually be switching to the second anioncomposition B₂. FIG. 4 shows a particle precursor which is produced by amethod wherein the first anion composition B₁ starts to be switched tothe second anion composition B₂ at a time different from that when thefirst cation composition A₁ starts to be switched to the second cationcomposition A₂. Hence, for the anions and the cations, the interface ofthe anions B₁ and B₂ does not coincide with the interface of the cationsA₁ and A₂.

In another embodiment, as shown in FIG. 2 , for the anions B₁ and B₂,since B₁ starts to be switched to B₂ from the first time t₁, andtherefore forms a shell which contains B₁ and B₂ with gradualconcentration, hence, there is a clear interface formed at the firsttime t₁ in the particle. For the cations, since there is only one cationA₁ fed into the reactor during the whole process, there is no clearinterface of A₁ in the particle.

In one embodiment, the gradient part in the shell initiates when B₁starts to be switched to B₂. In another embodiment, the slope change formulti-slope gradient particles undergoes the change when B₁ equals B₂.

The stream (e_(i) . . . z_(i)) includes additional solvents, surfaceacting agents or de-foaming agents. For example, the solvent is at leastone selected from ethanol, isopropanol, ionic liquids and so on. Thesurface acting agents may be alky sulfates such as sodium dodecylsulfate (SDS), alkyl trimethyl ammonia species such as cetyltrimethylammonia (CTAB), glycols, glycerides. The de-foaming agent is ethanol.

In one embodiment, dopant is also fed into the reactor. The dopantrefers to salts of metal elements other than Ni, Co and Mn, labeled as“Me”. In one embodiment, the dopant species is Al₂(SO₄)₃. As a dopantelement, Al³⁺ would be precipitated together with other cations. In suchembodiment, Al³⁺ can be added to the cathode particle precursor duringco-precipitation without using an additional chelating additive to slowthe precipitation kinetics. Further, in such embodiment, the cathodeparticle precursor is Ni-rich material in which a ratio between Ni andtransitional metal is larger than 0.7, and still includes the Al dopantwithout using an organic chelating additive. The thickness and depth ofAl³⁺ depositing into the particle precursor can be tailored andregulated based on the time when the anions start to be graduallyswitched and the time when feeding Al³⁺ thereinto.

Solids with different cation-anion pairings have different equilibriumsolubilities, as is tested by the solubility product, Ksp. Duringprecipitation the Ksp value is the thermodynamic limit of metal ionsprecipitating out of solution, with different anions and pH having aninfluence. By adjusting the solution pH and anion, the precipitationspossible and the stability of said cations in the solid form isadjusted, which is desirable for cathode precursor particles to bettercontrol the selection of dopants available for use during aco-precipitation reaction.

The pH of each precipitation zone is maintained at a range of 7-13. Inone embodiment, the pH is at a range of 9.5-12.5 when precipitatinghydroxides and at a range of 7-10 when precipitating carbonates.

In one embodiment, the pH is constant regardless of the anion speciesbeing fed for the co-precipitation. In another embodiment, the pH startsto be changed at the time when the first anion composition B₁ starts tobe gradually switched to the second anion composition B₂.

The precipitation zone agitated vessel is well mixed during the feeding,and has a Re>6,400, with a mixing time from 0 to 1,200 seconds. In oneembodiment, the mixing time is 0 to 120 seconds. In another embodiment,the mixing time is 0 to 45 seconds. The precipitation zone temperatureis maintained between 30 and 80° C. In one embodiment, the precipitationzone temperature is maintained between 45 and 60° C.

Table 1 shows the solubility product constant (K_(sp)) of carbonate andhydroxide materials. As can be seen from table 1 that the solubilityproduct constant (K_(sp)) of carbonate is larger than that of hydroxide.Theoretically, more hydroxide materials precipitate than the carbonatematerials under the same pH. The K_(sp) and pH are usually two mainfactors determining the solubility of a substance. In table 1, “(II)”means a valence of the metal element in the precipitation is divalent.

TABLE 1 Solubility Product Constants near 25° C. Ionic Compound K_(sp)Ionic Compound K_(sp) Aluminum hydroxide 1.3 × 10⁻³³ Aluminum carbonate(not stable) N/A Cobalt(II) hydroxide 1.6 × 10⁻¹⁵ Cobalt(II) carbonate1.4 × 10⁻¹³ Magnesium hydroxide 1.8 × 10⁻¹¹ Magnesium carbonate 3.5 ×10⁻⁸  Manganese(II) hydroxide 1.9 × 10⁻¹³ Manganese(II) carbonate 1.8 ×10⁻¹¹ Nickel(II) hydroxide 2.0 × 10⁻¹⁵ Nickel(II) carbonate 6.6 × 10⁻⁹ 

In another embodiment, the pH is constant regardless of the anionspecies being fed for the co-precipitation. In such embodiment, both thefirst anion composition B₁ and the second anion composition B₂ have aconstant and same pH, for example, at a range of 9-10.5.

In some embodiments, the pH changes during the time period that theanion composition switches from B₁ to B₂. For example, the pH changesduring the time period when hydroxide is switched to carbonate, sincethe first anion composition B₁ is hydroxide which has a pH of 10-14, andthe second anion composition B₂ is carbonate which has a pH much lower.

In some embodiments, the pH gradually changes during the entirereaction, or for a specified duration of the reaction.

After sufficient time till the precipitation ends, the precipitationparticles are deposited from the precipitation zone to from a particleslurry, which is collected in a hold-up tank or directly fed to asolid-liquid filtration device to obtain precipitated particles. Thefiltration device may be a plate and frame filter, candlestick filter,centrifuge, vacuum drum filter, pressure drum filter, hydrocyclone,nutsche filter, clarifier or some combination of devices. Next, thefiltered precipitated particles (i.e., the filter cake) are washed toremove byproduct salts from the precipitation reactions.

And then, the precipitated particles are dried under vacuum at anatmosphere of N₂, Ar or air for 3-24 hours between 80-200° C., thusforming the precipitated particles precursor.

Once dried, the precipitated particles precursor is contacted and wellmixed with a lithium source to form a mixture. The lithium source isselected from lithium hydroxide (i.e., LiOH), LiOH·H₂O, lithiumcarbonate (Li₂CO₃), LiNO₃, lithium acetate, lithium metal or Li₂O. Inone embodiment, the lithium source is lithium hydroxide. In anotherembodiment, the lithium source is lithium carbonate.

In one embodiment, a mole ratio between Li from the lithium source andthe metal cation from stream (a) is in a range of 0.5-1.5. In anotherembodiment, the mole ratio is 0.9-1.15. In still another embodiment, themole ratio is 1.01-1.10.

After the lithium source and the precipitated particles precursor aremixed uniformly to form a mixture, calcine the mixture under atemperature of 300-950° C., wherein multiple hold temperatures and ramprates may be used. For example, firstly controlling the temperature at300-500° C. for 2-20 hours, and then raising temperature to 700-850° C.and maintaining for 2-20 hours. The ramp rate during heating is from 0.5to 10 degrees per minute. In another embodiment, the ramp rate duringheating is 2-5 degrees per minute. The calcination time is from 2 hoursto 48 hours.

During calcination in the method above, water may generate between0-800° C. during the calcining step. Since during calcination, theprecursors underwent decomposition and/or oxidation to yield theexpected products, the cathode active particles. During the calciningstep, the following reaction occurred based on formulas 1-3, whereinM(OH)₂, M(CO₃) and M(C₂O₄) may be one of the precipitated particles fromthe solution, M refers to metals:M(OH)₂=MO_(x)+H₂O  (formula 1)M(CO₃)=MO_(x)+CO/CO₂  (formula 2)M(C₂O₄)=MO_(x)+CO/CO₂  (formula 3).

Tables 2 and 3 show moles of water evolved from calcination of 1 mol ofM(OH)₂/MCO₃ precursor (i.e., lithiation process) when using differentlithium source. We can get that while the exact water release iscomplicated by the choice of lithium source, it is apparent thathydroxide precursor particles will generate water while carbonate andoxalate anion presence will result in some carbon-oxide species.

TABLE 2 Moles of water evolved from calcination of 1 mol M(OH)₂/MCO₃precursor when the lithium source is LiOH•H₂O 1 mol M(OH)₂/MCO₃M(OH)₂/MCO₃ M(OH)₂/MCO₃ M(OH)₂/MCO₃ precursor M(OH)₂ MCO₃ (1:1) (1:1)(1:1) (1:1) lithiation Water evolved from calcination (mol)  90% 2.25mol 1.35 mol 1.80 mol 1.95 mol 2.03 mol 2.07 mol 100% 2.50 mol 1.50 mol2.00 mol 2.17 mol 2.25 mol 2.30 mol 103% 2.58 mol 1.55 mol 2.06 mol 2.23mol 2.32 mol 2.37 mol 110% 2.75 mol 1.65 mol 2.20 mol 2.38 mol 2.48 mol2.53 mol 120% 3.00 mol 1.80 mol 2.40 mol 2.60 mol 2.70 mol 2.76 mol 130%3.25 mol 1.95 mol 2.60 mol 2.82 mol 2.93 mol 2.99 mol

TABLE 3 Moles of water evolved from calcination of 1 mol M(OH)₂/MCO₃precursor when the lithium source is Li₂CO₃ 1 mol M(OH)₂/MCO₃M(OH)₂/MCO₃ M(OH)₂/MCO₃ M(OH)₂/MCO₃ precursor M(OH)₂ MCO₃ (1:1) (1:1)(1:1) (1:1) lithiation Water evolved from calcination (mol)  90% 0.90mol 0.00 mol 0.45 mol 0.60 mol 0.68 mol 0.72 mol 100% 1.00 mol 0.00 mol0.50 mol 0.67 mol 0.75 mol 0.80 mol 103% 1.03 mol 0.00 mol 0.52 mol 0.69mol 0.77 mol 0.82 mol 110% 1.10 mol 0.00 mol 0.55 mol 0.73 mol 0.83 mol0.88 mol 120% 1.20 mol 0.00 mol 0.60 mol 0.80 mol 0.90 mol 0.96 mol 130%1.30 mol 0.00 mol 0.65 mol 0.87 mol 0.98 mol 1.04 mol

The content of water evolved from the cathode particle precursor and Liprecursor will be decreased when an anion composition gradient materialis prepared, because CO/CO₂ will be evolved partially during thedecomposition reactions instead of H₂O, just as formulas 2 and 3 show.

The calcination is conducted under atmosphere selected from N₂, air,dried air, oxygen or some combination thereof. The calcinationtemperature is critical for concentration gradient materials, since toohigh, too long, or a combo of the two may cause so much cation diffusionthat a gradient is no longer present in the final cathode activeparticles.

To characterize and analysis the precipitated cathode active particleswhich have concentration gradient elements, SEM, porosimetry, pycnometerand particle size distributions can be utilized. The presence of aconcentration gradient can be confirmed by depth profiling a particle orvia cross-sectioning a particle and using an EDS line scan or electronmicroprobe analyzer.

The precipitated and cathode active particles can be characterized usingthe particle size distribution D10, D50, D90 or the Sauter mean diameterd₃₂. The Sauter mean diameter d₃₂ can be calculated by the formula

${d_{32} = \frac{\Sigma_{k = 1}^{N}n_{k}d_{k}^{3}}{\Sigma_{k = 1}^{N}n_{k}d_{k}^{2}}},$wherein “n_(k)” is the relative fraction and “d_(k)” is the bin diameterfrom the particle size distribution. The particle size distribution canbe collected via a light scattering instrument. In one embodiment, theprepared cathode active particles have a Sauter mean diameter at a rangeof 0.5-30 μm. In another embodiment, the Sauter mean diameter is at arange of 1-15 μm.

The porosity of the prepared cathode active particles can be analyzedusing BET and BJH analysis.

The prepared cathode active particles can be used in lithium-ionbattery, in which the prepared cathode active particles include Li andtransitional metals. In detail, in one embodiment, the prepared cathodeactive particles are mixed with a binder and conductive particles toform a mixture slurry. The mixture slurry is further cast onto ametallic foil to form a cathode electrode. The cathode electrode can beused in a lithium-ion battery.

To test the cathode material performance, galvanotactic charge-dischargetests can be performed. The material capacity, cycle retention, rateperformance and cycle efficiency can all then be determined.

Example 1

FIG. 1 shows a schematic view of the reaction device to form the cathodeactive particles. As shown in FIG. 1 , the reaction is conducted withthe following steps: Firstly, placing a 10 L glass reactor into ajacketed stirred tank, filling the glass reactor with 3 L of 0.5M aquaammonia and stirred at 500 rpm. At the same time sparging N₂ gas throughthe solution to remove oxygen from the water and headspace of thereactor, and controlling the temperature of the solution to 50° C. viacirculating hot water through the jacket. Meanwhile, in order to controlthe pH of the solution, feeding a 10.6M NaOH solution with a pHcontroller at set-point 10.7.

And then, pumping a 2M 90:10 Ni:Co metal sulfate solution (the firstcation composition A₁) into the reactor at a flowrate of 125 mL/hr and a9.6M aqua ammonia solution at a flowrate of 20 ml/hr. Proceeding thefeeding for 21.3 hrs, and then ceasing the metal sulfate and aquaammonia feeds. Particle slurry was formed in the reactor.

Optionally, filtering to remove the liquids and washing the particleslurry using a Buchner funnel until the filtrate conductivity was below100 mS, at which point the wet Ni:Co 90:10 filter cake was placed into acontainer with a constant N₂ cover. Such step would facilitate thehydroxide anion to grow directly in the core. Next, feeding 3 L of 0.2Maqua ammonia solution into another 10 L glass reactor, sparging with N₂gas into the solution to remove oxygen therein. And then, adding 19 wt %of the collected Ni:Co 90:10 filter cake to the solution. Heating thesolution to 50° C. while stirring at 500 rpm. These steps are optional.

And then, pumping a 2M Ni:Mn:Co 6:2:2 metal sulfate solution into thereactor at a flowrate of 125 mL/hr for the first 3.2 hrs. Concurrentlypumping a 1.5M sodium carbonate solution, the feeding of the sodiumcarbonate starting with 400 mL of liquid at 0.5 mL/min into a tankoriginally containing 400 mL of 3M sodium hydroxide. Pumping The tankoriginally containing sodium hydroxide was pumped into the reactorcontinuously at 1 mL/min. Separately, the 3M NaOH solution wascontrolled by a metering pump to maintain the reactor pH. The reactor pHset-point started at 9 and was decreased by 0.2 every hour.

At 3.2 hours, the pH control solution was switched from 3M sodiumhydroxide to 1.5M sodium carbonate, and 0.64 mol of aluminum sulfatepowder was added to the transition metal sulfate Ni:Mn:Co 6:2:2solution. All other flows remained the same into the reactor. At 6.4hrs, the flows and stirring for the reactor were stopped. The particleslurry was filtered and washed. The filter cake was dried at 100° C.under nitrogen overnight before being characterized.

In order to make the feeding clearer, table 4 lists partial materialsadded in partial stage and their relevant information provided by themethod of example 1.

TABLE 4 partial materials and relevant information in example 1 concen-tration flowrate time amount Materials added Ni:Mn:Co 6:2:2   2M 125mL/hr 3.2 hrs / Sodium carbonate  1.5M 0.5 mL/min / 400 mL NaOH 10.6M 1mL/min / / NaOH (pH controller)   3M / / / Materials added 3.2 hrs laterNi:Mn:Co 6:2:2   2M 125 mL/hr 3.2 hrs / Sodium carbonate  1.5M 0.5mL/min / 400 mL NaOH 10.6M 1 mL/min / / Sodium carbonate  1.5M / / / (pHcontroller) Aluminum sulfate 0.64 mo1 / / / (dopant)

To verify the particle structure, a Hitachi SU8010 SEM that is able touse a focused ion beam to cross-sectional particles was used to studythe particle structure. After cross section, EDS was used to determinethe relative locations of elements within the sample particles studied.FIG. 6 shows the spots on the cross section of one particle precursorfor ED observation, wherein triangles indicates the locations of EDSdata collection region. Table 5 shows the elemental analysis results oncross-sectional particle precursor in example 1. FIG. 7 shows carbonsignature of EDS line scan of the cross-sectional particle precursor ofExample 1, wherein carbon is derived from a component of the sodiumcarbonate anion. In FIG. 7 , the character “C” means carbon, and “K”after “C” is an alpha radiation signature.

TABLE 5 Results of EDS elemental analysis on precursor particle ofExample 1 EDS Spot EDS Spot 1 EDS Spot 2 EDS Spot 3 Weight Atomic WeightAtomic Weight Atomic Element % % % % % % C 3.48 8.60 3.79 8.72 6.6715.13 O 31.44 58.27 34.69 59.95 30.11 51.28 Al 0.37 0.41 3.81 3.91 7.087.15 Mn 1.81 0.98 8.55 4.30 12.57 6.23 Co 6.28 3.16 12.53 5.88 11.805.46 Ni 56.61 28.59 36.62 17.25 31.77 14.75

From table 5 we can get that the Al content increases near the surface.Meanwhile, table 5 also shows that the carbon content increase near thesurface. FIG. 7 shows a carbon signature of EDS line scan ofcross-sectional particle precursor of example 1. As shown in FIG. 7 ,the carbon signature is strongest at the location where the distance of15, and at the distances around 8-15 the carbon signature graduallybecomes stronger. Since carbon is derived from sodium carbonatesolution, the data in table 5 and FIG. 7 is consistent with the stepsfor forming the particle with a concentration gradient within theparticle.

In view of the above, the method of the present disclosure has thefollowing advantages:

Firstly, since different cations can be precipitated with differentanions separately, the transition metal dopants other than Ni, Co and Mncations that are incompatible with the core anion species under theprocessing conditions can be easily added to the particle precursor inthe shell. And vice versa, wherein cations or other dopants that canonly be compatible with the core anion under the processing conditionscan be added to the particle before switching to an incompatibleprocessing location for the shell. Particularly, Al³⁺ can be added tothe particle precursor during the co-precipitation under the premisethat there is hydroxide in the solution which can form precipitationwith Al³⁺; in such conditions, no additional organic chelating additivesare needed to remove Al³⁺, and the precipitation kinetics are avoided tobe slowed without chelating agents. Because of this, Ni-rich particlesprecursor can have Al dopant into the particle without using organicchelating additives, the Ni-rich particles precursor has a mole ratio ofNi to transitional metals higher than 0.7. The concentration of Al³⁺deposited into the particles can be adjusted based on the time feedingthe Al³⁺ dopants and the time when switching the anions.

Secondly, no matter where the gradient portion is located, in the coreor in the shell, the concentration gradient of the anion species ensuresthat there is smooth transition between different anion species, thatis, the transition from the former anion to the latter is not a sharpchange, but a gradual switching. Because of this, the gradient portionendows the particle precursor a gradient surface, which makes thetransition from the portion having only the first anion to the portionhaving both the first and second anions becomes more smoothly. Theparticle precursor is more solid during later processing, and cracks ordelamination would not occur. This has great improved the duration andlife-span of the cathode particles prepared based on the particleprecursor.

Thirdly, due to the feeding of elements Ni, Mn, Al etc. into thereaction, the cobalt content will be below 20% of the total transitionmetal ratio, and preferably below 5%, and more preferably 0% cobalt willbe present in the cathode precursor particle. Because of this, the costis greatly decreased.

Fourthly, during calcination, anions of CO₃ or C₂O₄ would evolve CO/CO₂gas, which makes non-homogeneous porosity within the particles. Sincethe concentration of the anions are gradually changed, the porositywithin the particles would also be gradually increased, especially nearthe surface of the particles. Hence, the material may have improvedtransport properties during high rate electrochemical testing.

Fifthly, the content of water evolved from the cathode particleprecursor and Li source will be decreased when an anion compositiongradient material is prepared, because CO/CO₂ will be evolved partiallyinstead of H₂O during the decomposition reactions.

INDUSTRIAL APPLICABILITY

The method of the present disclosure can prepare transitional-metalparticle precursor and cathode active particles under co-precipitationreaction. The particle precursor has a core-shell structure, the coreand the shell are made of different anions. Such cathode active particlecan be used to prepare cathode of lithium-ion battery.

What is claimed is:
 1. A method for preparing a core-shell structuredparticle precursor, comprising the following steps: from an initial timet₀ to a first time t₁, feeding a first anion composition B₁ through afirst container into a reactor, and feeding a first cation compositionA₁ through a second container into the reactor, the first anioncomposition B₁ and the first cation composition A₁ reacting andprecipitating in the reactor, t₁ comes after to, t₀=0; at the first timet₁, the first container is full of the first anion composition B₁, andthe second container is full of the first cation composition A₁; feedinga second anion composition B₂ through a third container into the firstcontainer and feeding the second anion composition B₂ and the firstanion composition B₁ through the first container into the reactor fromthe first time t₁ to a second time t₂, t₂ comes after t₁, during whichthe first anion composition B₁ is gradually switched to the second anioncomposition B₂ wherein the first anion composition B₁ is hydroxidesalts, and the second anion composition B₂ is at leaset one selectedfrom the group consisting of carbonate, oxalate, or a cominationthereof; and feeding at least the first cation composition A₁ throughthe second container into the reactor from the first time t₁ to thesecond time t₂, thereby forming a precipitated particle slurry; andfiltering, and drying the precipitated particle slurry to yield theparticle precursor; wherein instantaneous concentration of anions beingfed into the reactor from the first time t₁ to the second time t₂ can bedescribed as:${B = \frac{{B_{i}V_{i}} + {\left( {{F_{B2}B2} - {B_{i}F_{B}}} \right)\left( {t_{i + 1} - t_{i}} \right)}}{V_{i + 1}}},$wherein: B is the instantaneous concentration of anions being fed intothe reactor; B_(i) is the anion concentration at time t_(i) that existsin the first container; V_(i) is the volume of solution at time t_(i)that exists in the first container; F_(B2) is the flowrate from thethird container into the first container; B2 is the anion concentrationin the third container; F_(B) is the flowrate from the first containerinto the reactor; t_(i+1) is time at moment i+1; t_(i) is time at momenti; V_(i+1) is the volume of solution at time t_(i+1) that exists in thefirst container.
 2. The method of claim 1, wherein the first anioncomposition B1 and/or the second anion composition B₂ has aconcentration 0.001-14 mol anion/L; and/or the first cation compositionA₁ has a concentration 0.001-6 mol cation/L.
 3. The method of claim 1,wherein the first anion composition B1 and/or the second anioncomposition B2 is at least one selected from the group consisting ofNaOH, Na₂CO₃, NaHCO₃, Na₂C₂O₄, LiOH, Li₂CO₃, LiHCO₃, Li₂C₂O₄, KOH,K₂CO₃, KHCO₃, K₂C₂O₄, or combination of the species; and/or the firstcation composition A₁ is at least one selected from the group consistingof Mg, Ca, Zr, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Al, in a form of sulfate,carbonate, chloride, nitrate, fluoride, oxide, hydroxide, oxyhydroxide,oxalate, carboxylate, acetate, phosphate or borate.
 4. The method ofclaim 1, wherein method further comprises the following step: feedingthe second anion composition B₂ and the first cation composition A₁ intothe reactor from the second time t₂ to a third time t₃, t₃ comes aftert₂.
 5. The method of claim 1, wherein during the initial time t₀ to thesecond time t₂, the first cation composition A₁ is the only cation thatis fed into the reactor.
 6. The method of claim 1, wherein from theinitial time t₀ to the first time t₁, the first cation composition A₁ isfed through the second container into the reactor; and feeding a secondcation composition A₂ through a fourth container into the secondcontainer and feeding the second cation composition A₂ and the firstcation composition A₁ through the second container into the reactor fromthe first time t₁ to the second time t₂, during which the first cationcomposition A₁ is gradually switched to the second cation compositionA₂.
 7. The method of claim 1, wherein from the initial time t₀ to aswitching time t_(s), the first cation composition A₁ is fed through thesecond container into the reactor, t_(s) is between the first time t₁and the second time t₂; and from the switching time t_(s) to the secondtime t₂, feeding a second cation composition A₂ and the first cationcomposition A₁ through the second container into the reactor, duringwhich the first cation composition A₁ is gradually switched to thesecond cation composition A₂.
 8. The method of claim 1, wherein thefirst cation composition A₁ and the second cation composition A₂ has acation ratio of Ni_(x)Mn_(y)Co_(z)Me_(1-x-y-z), where x+y+z≤0.9, z≤0.2,“Me” is at least one additional metal elements selected from the groupconsisting of Mg, Ca, Zr, Ti, V, Cr, Fe, Cu and Al.
 9. The method ofclaim 1, wherein a pH during the reaction is 7-13 which is graduallychanged, the pH is 9.5-12.5 when precipitating hydroxides, the pH is7-10 when precipitating carbonates; and/or a temperature during thereaction is 30-80° C.
 10. The method of claim 1, wherein the step thatthe first anion composition B₁ is gradually switched to the second anioncomposition B₂ comprises the following steps: at the first time t₁, thefirst container is full of the first anion composition B₁; graduallyfeeding the second anion composition B₂ from the third container intothe first container from the first time t₁ to the second time t₂, suchthat the first anion composition B₁ and the second anion composition B₂form a dynamic mixture in the first container; feeding the dynamicmixture through the first container into the reactor from the first timet₁ to the second time t₂; at the second time t₂, the first container ismainly full of the second anion composition B₂.
 11. The method of claim6, wherein the step that the first cation composition Ai is graduallyswitched to the second cation composition A₂ comprises the followingsteps: at the first time t₁, the second container is full of the firstcation composition A₁i; gradually feeding the second cation compositionA₂ from the fourth container into the second container from the firsttime t₁ to the second time t₂, such that the first cation composition A₁and the second cation composition A₂ form a dynamic mixture in thesecond container; feeding the dynamic mixture through the secondcontainer into the reactor from the first time t₁ to the second time t₂;at the second time t₂, the second container is mainly full of the secondcation composition A₂.
 12. The method of claim 7, wherein the step thatthe first cation composition Ai is gradually switched to the secondcation composition A₂ comprises the following steps: at the switchingtime t_(s), the second container is full of the first cation compositionA₁; gradually feeding the second cation composition A₂ from the fourthcontainer into the second container from the switching time t_(s) to thesecond time t₂, such that the first cation composition A₁ and the secondcation composition A₂ form a dynamic mixture in the second container;feeding the dynamic mixture through the second container into thereactor from the switching time t_(s) to the second time t₂; at thesecond time t₂, the second container is mainly full of the second cationcomposition A₂.
 13. The method of claim 8, wherein the first cationcomposition A₁ has a cation ratio of Ni_(x)Mn_(y)Co_(z)Me_(1-x-y-z),where x+y+z≥0.9, 0.75≤x≤1; 0≤0.1;; and/or the second cation compositionA2 has a cation ratio of Ni_(x)Mn_(y)Co_(z)Me_(1-x-y-z), wherex+y+z≥0.9, 0.3≤x≤0.7; 0.25≤y≤0.5, “Me” is at least one additional metalelements selected from the group consisting of Mg, Ca, Zr, Ti, V, Cr,Fe, Cu and Al.